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LG LFC23760ST - Freezer freezes okay - Fridge does not cool

rcurry71

Premium Member
Joined
Jan 25, 2018
Messages
4
Location
48842
Model Number
LFC23760ST
Brand
LG
Age
6-10 years
The evaporator fan is not running, and therefore the fridge does not get cool. The freezer is working fine. I opened it up and cleared off all the ice (apparently it was not defrosting like it should) and dried the crap out of the evaporator fan with a blow dryer. Did not work. I did some research and I ran Test Mode 1 and the fan ran for maybe 10 seconds, and then stopped. After maybe 10 seconds it did it again. This happened 4 times and then stopped for good. The service Manual states that the fan should run continuously when testing Mode 1. Literally while typing this, I caught the fan running like this again, where it would run for 10 seconds a few times and then stop for good. Any thoughts as to why the fan would act like this and not stay on?

Thanks for any advice/help you can provide!
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
38,748
Location
Murray, Utah 84107, United States

rcurry71

Premium Member
Joined
Jan 25, 2018
Messages
4
Location
48842
Thanks. Should it be 12-14VDC at ALL times, or only when the fan should be on?

I tested it and at first it read 0V. I am new at this stuff so, knowing that the fan previously would come on when first plugged in, I unplugged the fridge, waited 30 seconds, and plugged it back in. At first it read 16V and then dropped 1V every 10 seconds or so until it ended up at 0V.

Notes from the schematics:
Fan motor driving circuit (freezing compartment fan)
- The circuit makes the Motor Fan OFF by cutting Off the power supplied to driver inside the Fan Motor when it is necessary.
- This is a circuit to perform a temporary change of speed for the fan motor and applies DC voltage up to 7.5V ~ 16V to motor.
- This circuit prevents over-driving the fan motor by cutting off power applied to the fan motor in the lock of fan motor by sensing the operation RPM of the fan motor.​

I am not sure what to make of your suggestion of 12-14VDC, the second point above of 7.5V ~ 16V, and then a chart (cannot show here) that says pin 6 should be 13V-15V when the motor is on.

There is a third wire that 'reads' RPM of the motor and is used to adjust fan speed. Is it possible that since the fan is not running (I unplugged the connector for testing) and not sensing the motor RPM, that maybe it is reducing the amount of VDC, or is this a bad PCB? Am I over-thinking this?

Thanks!
 

rcurry71

Premium Member
Joined
Jan 25, 2018
Messages
4
Location
48842
Sorry to hit you up with 2 replies before you've had a chance to answer the first, but I was wondering about the lack of defrosting. I am assuming a bad PCB board would not control the heater correctly and ice would form. Would the same happen with a non-functioning fan?

Thanks again!
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
38,748
Location
Murray, Utah 84107, United States
OK, it sounds like the main board is bad. I don't have a wiring diagram or tech sheet for your model so I'm using experience and a wire diagram for a similar model. Your tech sheet says 7.5 to 16, which is 7.5 for low speed and 16 for high speed, and since the compartment is not cold enough I know the fan should be on high speed, any reading above 12 VDC would tell me the fan motor is the problem. So 12-14 or 13-15 doesn't really matter at this point, you have 0 VDC.

When the fan motor stops working there's no airflow across the evaporator. That will cause excessive frost build up on the coils. The defrost system is most likely OK. It's rare to have more than one part fail at the same time. I would replace the main board. If you want to post a copy of your wire diagram and tech sheet I'll be happy to take a look at it and see if I missed anything.
 
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